1. Field of the Invention
This invention relates to a powertrain of hybrid electric vehicles, particularly to a powertrain module that can be installed between and secured to an engine output and a transmission input.
2. Description of the Prior Art
Hybrid electric vehicles (HEVs) have both an internal combustion engine and an electric machine, which are alternately, or in combination, used to propel the vehicle. A variety of different powertrains are used in hybrid vehicles such as a parallel configuration, in which the engine is connected to the motor by a disconnect clutch with the motor driving a torque converter input of an automatic power transmission. The transmission has an output which is connected to a differential coupled to the two driven wheels of the vehicle.
A need exists in the industry for a hybrid electric powertrain that includes a modular subassembly for use with a variety of engines and transmissions, such that the module can be installed between and secured to an output of one of a number of engines and to an input of one of a number of transmissions. The assembled powertrain may then be employed in a variety of vehicles. The module should include a hydraulically actuated disconnect clutch, the electric machine and suitable power paths between the engine and electric machine to the transmission input. Preferably, the module provides for hydraulic communication from the transmission's hydraulic system to the clutch, a balance dam and the electric machine. The module must provide an oil sump containing hydraulic fluid delivered to the module, and a path for continually returning that fluid to the transmission's oil sump so that the transmission pump is continually supplied reliably with fluid.
The module should require low manufacturing and assembly costs, no vehicle body modification, and reliable performance.
This module is sometimes call a front module (FM), since it is part of the MHT and is bolted in front of the transmission. Since this module is purely a length addition to the base powertrain, it is desired to make the module as short as possible. The connection between the engine and the FM usually has a damper to protect the FM input shaft spline from engine torsional vibrations. The damper adds length and cost of the powertrain.
The damper has a natural frequency that is passed through every time the engine starts and stops. The damper also increases powertrain inertia protentially reducing fuel economy and performance.